1. Field of the Invention
The present invention relates to a head-up display system, and in particular to a head-up display system in which there are displayed image data individually, which are the same or different, on both sides of a combiner provided in a part of an upper portion of a glass window or door of a bus, train or shop, thereby providing information to customers or passengers both inside and outside the shop, train or the like.
2. Description of the Prior Art
A head-up display system (referred to a HUD hereinafter) is an apparatus for use in a cockpit of an aircraft or in other various field. By providing such a HUD for example in a cockpit in an aircraft, it becomes possible for a pilot to confirm necessary information without turning his eyes from his operating direction to a dashboard direction. Such a HUD has been proposed in the prior art and reference may be made to U.S. Pat. No. 3,737,212 in 1973 and U.S. Pat. No. 4,218,111 in 1980 for a better understanding of such proposals. On the other hand, for increment of optical efficiency of a light source and combiner in a HUD, as is described in the "DIFRACTION OPTICS HEAD-UP DISPLAY TECHNOLOGY," reported by MARTIN WEIHRAUCH and ROBERT A. L OHMANN, SID 80 DIGEST, there is utilized a light source emitting green light with a sharp spectral distribution together with a combiner which has a high reflectivity with respect to this green light and which attenuates green light from the external view, thereby improving the brilliancy or definition of a picture of image data developed on the combiner in a HUD with enhancement of efficiency in association with the quantity of light.
However, in such a conventional HUD, there is provided a display of image data necessary for the operator superimposed on the real world scene in the pilot's forward visual field. That is to say, the image data is combined with the data of the external view in the forward direction of the pilot, and the combined image data can be seen using the two eyes of the observer alone. There is no idea, in the conventional HUD, that a plurality of image data are divided into two directions through a combiner so as to be individually displayed on the dual sides of the combiner in such a manner that the customers or passengers in the dual sides thereof can confirm the displayed picture of the image data.
Moreover, when a picture of projected image data is developed on one side of the combiner based on the reflection light beam reflected by the combiner and another picture of the same or different image data is developed on the other side of the combiner based on the transmission light beam transmitted through the combiner, both of the two pictures are respectively displayed on the dual sides of the combiner so as to be viewed by customers or passengers present in the dual directions with respect to the combiner, and in this case, the original image data of the projected image in the direction of the reflection light with respect to the combiner must be laterally reversed for the customers to read the picture of the projected image correctly because the picture of the virtual image formed by the reflection light with respect to the combiner is laterally reversed. Also, it is required to provide a total reflection mirror for totally reflecting the laterally reversed image, in other words, the system must be provided with two series of units independent of each other for preventing occurrence of a crosstalk or superimposition between the projected image in the direction of the transmission light and that of the reflection light, resulting in a large scale of the system and deteriorating or contaminating the quality of the projected image.
Moreover, there is another problem that, when the positions of the eyes of the observes in the respective sides of the combiner are apart from the position of the optical lens system of the HUD, the range of the projected image to be seen becomes narrow. Therefore, it is required to provide an optical lens system with a large aperture, resulting in increasing the cost thereof and being large in size thereof.